Tweva, you can buy 4’x8′ panels that are reflective on one side and are made from foam. The foam can go the outside or inside. Hot climates put shiny side out and vice versa in cold climate. You can then put 1/8th sheets of prefinished paneling on top of that. This also can be done on the ceiling. You can buy long, prefinished nails that will through the panels and foam board directly into the studs.
One thing to do first is spray the entire inside with Timbor (link below) as this is the best bug killer going but it does not work in wet areas.